1. Field of the Invention
This invention relates to surgicomedical prostheses in general, and in particular, to a total temporomandibular joint replacement system, including a temporal implant and a mandibular implant.
2. Description of the Related Art
Disease of the temporomandibular joint (TMJ) is often undiagnosed or misdiagnosed because it mimics many different diseases and has such a wide variety of symptoms..sup.1
.sup.1 Morgan, D. H., "The Great Imposter--Diseases of the Temporomandibular Joint;" JAMA, vol. 235, p.2395, May, 1976.
Most people who have this problem suffer from a myo-facial pain-dysfunction syndrome primarily as a muscle problem related to dental or skeletal malrelationships and tensional factors, or in some cases, as a reversible irritation in the joint. Most of these patients can be successfully treated using nonsurgical techniques. The remaining individuals usually have organic disease within the joint, usually osteoarthritis, and the latter often require some form of surgical treatment.
Much of the TMJ surgery that has been performed to date has been the result of pathological arthritic changes within the joint, e.g., ankylosis, a bony or fibrous fusion of the condyle (ball) to the mandibular fossa (socket). The surgical technique most commonly employed for treatment of this condition is essentially a form of osteoarthrotomy. Other surgical techniques, variously favored for symptoms other than ankylosis, include condylectomy, high condylelctomy, condylotomy, eminectomy, zygoectomy, meniscectomy, meniscus replacement and/or repair, and placement of various implants..sup.2
.sup.2 House, L. R., et al; "Temporomandibular Joint Surgery: Results of a 14-Year Joint Implant Study;" Laryngoscope, vol.94, no.4, pp.534-538, Apr., 1984.
For many years, TMJ interpositional arthroplasty has been an accepted surgical modality in the treatment of severe ankylosis. Typically, an osteotomy is performed at or below the line of the joint, and this may be accompanied by a partial or total diskectomy. In such procedures, it has been common to utilize some form of implant or prosthesis, either within the fossa or upon the condylar stump, or both, in order to restore approximately correct anatomic interpositional fit, if not function.
In the past, the implantation of metal fossa has been a commonly used technique for treatment of ankylosis. One such type of implant is described by R. W. Christensen in U.S. Pat. No. 3,178,728. This prosthesis is contoured to fit within the glenoid fossa and overlay the articular eminence, and has been successfully employed in a relatively large number of cases.
However, in order to ensure a good fit between the prosthesis and the glenoid fossa, i.e., one which does not disturb the relation of the teeth and bite, it was necessary to provide these implants in up to 60 different sizes for each side, and a considerable amount of time was consumed in fitting them to the joint during surgery.
In U.S. Pat. No. 3,579,643, I disclosed an improvement over the preceding device in the form of a metallic articular eminence implant which was used for conditions other than ankylosis and which covered only the articular eminence of the temporal component of the joint. Since it was not designed to prevent a true bony or fibrous ankylosis from recurring, it was not necessary to cover the mandibular fossa portion of the joint. This permitted the provision of the device in only one size per side, although some surgical shaving of the eminence was occasionally required. Eventually, I found that, by having a variety of about ten sizes per side, the necessity of shaving of the eminences to arrive at a good fit could be reduced further.
The most popular material for interpositional arthroplasty implants has been a form of silicone rubber, e.g., Silastic.RTM., usually in the form of silicone rubber blocks or Dacron-reinforced sheaths of silicone rubber, primarily because of the material's biomedical compatibility or inertness, and because of its elasticity and the ease with which it can be worked and shaped to fit the anatomy of an individual patient's fossa. J. N. Kent, et al,.sup.3 describe a form of custom-fitted, laminated construction, glenoid fossa implant having a superior layer consisting of Proplast.RTM., a middle layer of Nomex.RTM. fabric impregnated with Teflon.RTM. FEP polymer, and an inferior layer of hard-fused Teflon TFE (Syncar.RTM.) polymer reinforced with graphite fiber disposed for articulation with the condyle. A variation of this implant is found in U.S. Pat. No. 248,665.
.sup.3 Kent, J. N., et al; "Temporomandibular Joint Condylar Prosthesis: A Ten-year Report; J. Oral and Maxillofacial Surgery, vol. 41, pp. 245-254, 1983.
Unfortunately, silicone rubber materials, when used alone or as a functioning joint, can result in the loss of good biomechanical fit and jaw function caused by long term creep and flow of the material,.sup.4 as well as pathological sequelae in the nature of destructive lesions of the mandibular condyle, in which the material becomes abraided by the passage over it of the rough condylar bone, thereby causing particles of the material to slough off and be dispersed into the surrounding tissue..sup.5 These particles, unless they become walled off by fibrous connective tissue, can result in a foreign-body giant cell reaction and reactive synovitis.
.sup.4 Kent, J. N., et al, supra, at p. 252.
.sup.5 Westesson, P. L., et al; "Destructive Lesions of the Mandibular Condyle Following Diskectomy with Temporary Silicone Implant;" Oral Surgery, pp. 143-150.
In addition to fossa prosthesis, TMJ surgical procedures often include some form of condylar prosthesis, either alone or as part of a total TMJ replacement. An early form of a condylar implant is found in U.S. Pat. No. 248,492, and comprised an all-metal prosthesis cast from a surgical alloy to include a nonanatomic head, a neck portion and a flattened shank portion which was coated with Proplast.RTM. and screwed to the lateral surface of the ramus for fixation. A report on the use of this and a similar type of condylar implant over a ten year period in which 109 prostheses were placed in 80 patients is given by J. N. Kent, et al..sup.6
.sup.6 Kent, J. N., et al, supra.
One of the problems with an all metal, non-anatomic condyle is its tendency to wear away the mandibular fossa in which it resides. In this regard, it is to be noted that the mandibular fossa does not normally act as part of the functioning joint, but rather, merely as a "garage" in which the condyle is "parked" when at rest. During functioning, the condyle translates over the "driveway" of the articular eminence. However, after a condylectomy, the attachment of the lateral pterygoid muscle, which translates the condyle over the eminence, is usually lost. A hinging motion of the condyle within the articular eminence then results, leading to a wearing away of the bony fossa by the non-anatomic metallic head, which is unable to spread the forces over the fossa as evenly as a natural condyle would. An instance wherein the head of a metallic condyle actually penetrated through the bony glenoid fossa and into the cranial cavity of a patient with rheumatoid arthritis is reported by J. N. Kent, et et al..sup.7
.sup.7 Id., at p. 250.
From the foregoing, it will be seen that a desirable total TMJ replacement system is one that includes a temporal component which combines the stiffness and hard wearing surface of the metallic fossae prostheses with the adjustability and ease of fit of the silicone rubber implants, while avoiding the latter's problems, as well as a condylar component which is as strong and as durable as the metallic prostheses, but which has a head of a softer, more anatomically-shaped material which would not tend to wear away the bony fossae and which spreads the wearing forces more evenly thereon. The present invention discloses a TMJ replacement system which provides these advantages.